Metallic powders



1 2,734,817 WTALLHQ PQWDERS Ralph A. Happe, Worthington, @hio, assignor, by mesne assignments, to Batteile Development Corporation, (10- lumbus, (Ethic, a enrporation of Ghio No Drawing. Application February Serial No. 279,899

4 Claims. (ill. 75-.5)

This invention relates to metallic powders. More particularly, it relates to the production of irregularly shaped metallic particles by the process of preparing an essentially two-phase solid metallic body and dissolving out one of the phases.

In recent years, the techniques of fabrication of metal articles, by what are known as powder-metallurgy" techniques, has become Widely used. Under these processes metallic particles, in the form of powders, are shaped into the configuration desired for the finished article under great pressure, and then sintered at a high temperature to increase the bond strength. The fabrication of many metal objects has been facilitated, and many of the shortcomings of the usual casting methods have been overcome.

At the present time, many of the powders available for such use are more or less spherical in shape. This is particularly true in the case of alloy powders. In forming these powders into desired shapes for fabrication, it is necessary to use binder material in order that the compacts may have the required green strength. Even with the use of such a hinder the green strength of these articles is sometimes so small that the articles are unable to withstand removal from the die and handling before sintering at a high temperature. For best results the powders should be irregular in shape and capable of interlocking when compacted.

It is, therefore, one of the objects of this invention to provide a method of making improved metallic powders.

It is another object of this invention to form metallic powders which are highly irregular in shape and may be compacted without the necessity of an excessive amount of binding material.

A further object of this invention is to provide materials for fabricating metal alloy articles in which the composition remains unchanged during the fabrication process.

Yet another object is to metallic alloy powders.

Other objects of this invention will be apparent from the following detailed description. 7

In general, this invention'comprisesthe combination of two metals having suficient liquid solubility or miscibility to permit casting without segregation, and yet which have little solid solubility and do not form intermetallic compounds.

The two metals are melted together and permitted to solidify. As the liquid solidifies, the metals separate into two phases, one of the metals being embedded in a matrix formed by the other metal. The embedded metal is in the form of dendritic particles. The matrix materials are then removed from this composite, leaving the remaining metal in the form of metallic powder having a highly irregular shape.

It should be understood that the term metal, as used herein, is intended to be broad enough to relate to metal alloys and solid solutions, as well as single metallic elements.

As previously stated, suitable metals for use in practicing this invention comprise those which are miscible in a liquid state but have little solid solubility in each other. Examples of suitable binarysystems of metals include copper and iron, aluminum and mercury, bismuth provide a method of making States Patent 2,734,817 Patented Feb. 14, 1956 and mercury, cadmium and lead, copper and chromium, copper and cobalt, manganese and lead, molybdenum and nickel, molybdenum and iron, silver and platinum, silver and titanium, silver and lead, tungsten and iron, tungsten and nickel, tungsten and cobalt, etc.

The process of this invention can also be used with systems comprising more than two metallic elements. An example of these is a copper matrix in which is dispersed a solid solution of iron and chromium. Additional alloying elements, such as nickel, molybdenum, etc, can be incorporated in the iron-chromium solution. Other combinations will be obvious to those skilled in the art.

The separation of the matrix material can be accomplished in several ways, as by immersion in chemical solutions, melting, dissolving by electrolysis, or other suitable methods.

As a specific example of this invention, a composite of 72 per cent copper, 25 per cent iron, and 3 per cent chromium, was formed into an ingot. After cooling, this ingot was immersed in a nitric acid solution contained in a glass vessel. When the copper had completely dissolved, it was noted that a layer of ironchromium dendrites had formed on the bottom of the vessel. These dendritic particles were separated by filtering, washed several times with water and alcohol, and then dried.

The resulting product was a fine stainless steel powder which was of a particle size in the range commonly used for powder-metallurgy synthesis, and having a composition of approximately 12 per cent chromium, the balance iron. This powder was highly irregular in shape. When compacted together, the particles interlocked and formed a compact having a very high green strength."

Although a specific example has been used to illustrate the practice of this invention, it is to be understood that the invention is not to be limited thereby, but only by the scope of the appended claims.

What is claimed is:

l. The method of making dendritic metal particles which comprises the steps of combining copper, iron, and chromium in a liquid state, cooling said combined metals to a solid state to form a predominantly copper matrix in which are embedded particles of an iron-chromium alloy, and removing said copper matrix.

2. The method of making dendritic metal particles which comprises the steps of combining in a liquid state copper, iron, chromium and at least one additional metal selected from the molybdenum, cooling said combined metals to a solid state to form a predominantly copper matrix in which are embedded particles of an alloy comprising iron, chromium and said additional metal, and removing said copper matrix.

3. Dendritic alloy iron and chromium.

4. Dendn'tic particles, said particles comprising iron, chromium, and at least one metal selected from the group consisting of nickel and molybdenum.

particles, said particles comprising References Cited the file of this patent UNITED STATES PATENTS Powder Metallur vol. 9; Selected Government Research Reports, page 54. Published in 1951 by H. M. Stationery Ofi'ice, London, England.

group consisting of nickel and 

1. THE METHOD OF MAKING DENDRITIC METAL PARTICLES WHICH COMPRISES THE STEPS OF COMBINING COPPER, IRON, AND CHROMIUM IN A LIQUID STATE, COOLING SAID COMBINED METALS TO A SOLID STATE TO FORM A PREDOMINANTLY COPPER MATRIX IN WHICH ARE EMBEDDED PARTICLES OF AN IRON-CHROMIUM ALLOY, AND REMOVING SAID COPPER MATRIX. 